The present invention relates to a character generator of video apparatus, such as a video cassette recorder or a television receiver, and more particularly to a section erasure control apparatus of a character generator capable of erasing a character which is displayed at a region except for a predetermined character display region of screen.
Conventionally, a video apparatus, such as a video cassette recorder and a television receiver is equipped with a character generator which can display a character with an on screen display (OSD) function.
According to the conventional character generator, however, there are often generated cases in which a character is erroneously displayed on screen or a character is displayed in a region other than a predetermined character display region on screen.
FIG. 1 illustrates a conventional character display apparatus for a video apparatus, such as a video cassette recorder or a television receiver, and displays an established character on screen.
The character display apparatus comprises a microcomputer 1 for controlling the display of the character; a key signal generator 2 for inputting a command signal for displaying the character from a key board or a remote controller to the microcomputer 1; and a character generator 3 for generating character signal and mixing the character signal with a video signal therein, in accordance with a control signal from the microcomputer 1.
The operation of the character display apparatus will hereinafter be described.
First, if an user gives a command signal for displaying a character to the microcomputer 1 utilizing the keyboard or the remote controller, the microcomputer 1 controls the character generator 3 in accordance with the command signal input from the key signal generator 2.
At this time, the character generator 3 generates a character signal and mixes the character signal with a video signal. The mixed signal is displayed on screen.
FIG. 2, illustrates a a conventional character generator which is equipped in the character display apparatus shown in FIG. 1. The character generator comprises a character size oscillator 11 for generating a clock signal as to the size of a character to be displayed on screen; a character display timing generator 12 for controlling the timing as to the display of the character, in accordance with the output signal from the character size generator 11; an input control part 13 for inputting a clock signal sck and a data signal SIN and separating the data signal from an address signal, in accordance with an external control signal CS; a data control part 14 for receiving the data signal separated from the input control part 13; an address control part 15 for controlling the store of the data signal outputted from the data control part 14, in accordance with the address signal separated from the input control part 13; a display data memory 16 for storing and outputting the character display data corresponding to addresses 0-239 output from the data control part 14, in accordance with an output signal from the address control part 15; a display control register 17 for storing and outputting the display control data corresponding to addresses 240-243 output from the data control part 14, in accordance with the output signal from the address control part 15; a display character read only memory (ROM) 18 for previously storing the fonts of a character to be displayed on screen and controlling the pattern of the character to be displayed output from the display data memory 16; a horizontal position counter 19 for counting the horizontal position of screen; a display position detecting part 20 for generating addresses of the character to be displayed, in accordance with an output signal from the character display timing generator 12 and the horizontal position counter 19; a read address control part 21 for controlling the character signal to be displayed controlling the display data memory 16, in accordance with the output signal of the display position detecting part 20; a shift register 22 for shifting an output signal from the display character ROM 18; a blanking part 23 for blanking the display of character to be displayed, controlling the shift register 22 in accordance with the display control register 17; a display control part 24 for controlling the display of the character with the output signal from the shift register 22; a video output part 25 for mixing the character signal output from the display control part 24 with a video signal and then outputting the mixed signal; a synchronization oscillator 26 for generating a synchronization signal; a synchronization timing generator 27 for controlling the timing of synchronization, in accordance with the output signal from the synchronization oscillator 26; and a synchronization signal switching part 28 for switching the output signal from the synchronization timing generator 27 and an external synchronization signal. The operation of the character generator will be hereinafter described.
First, the character size oscillator 11 outputs a clock signal as to the dot-size of the character to be displayed on screen. The character display timing generator 12 generates a timing signal for controlling the reading-timing of a character signal which is designated by the display data memory 16.
In case that the control signal cs is inputted with a low level potential, the input control part 13 inputs the clock signal sck and the data signal SIN and then separates them into a data signal and an address signal. The data signal is transferred to the data control part 14 and the address signal is transferred to the address control part 15.
The address control part 15 analyzes the address signal. As the result of analysis,the address control part 15 stores the data signal outputted from the data control part 14 in the display data memory 16 in case that the address is corresponding to addresses 0-239 and stores the data signal outputted from the data control part 14 in the display control register 17 in case that the address is corresponding to addresses 240-243.
On the other hand, the display control register 17 controls the blanking part 23 in accordance with blanking bits which are previously stored. The display data memory 16 outputs fonts corresponding to the character to be displayed on screen, and controls the display character ROM 18 in accordance with the data signal therein. The fonts output from the display character ROM 18 are transferred to the display control part 24 through the shift register 22.
The horizontal position counter 19 counts the horizontal position of display character with the output signal from the character display timing generator 12 and the read address control part 21 controls the output of character fonts from the display character ROM 18 and controls the display data memory 16 in accordance with the output signal from the horizontal position counter 19. The character fonts outputs from the display character ROM 18 are input to the video output part 25 and then mixed with the video signal therein. The video output part 25 outputs the signal in which the character fonts are mixed with the video signal.
The synchronization oscillator 26 oscillates to generate a clock signal and the synchronization timing generator 27 generates a horizontal synchronization signal and a vertical synchronization signal, in accordance with the clock signal. On the other hand, the synchronization signal switching part 28 controls the horizontal synchronization signal and the vertical synchronization signal outputted from the synchronization timing generator 27 and the external synchronization signals. In this character generator, it is very important to prevent a wrong operation due to static electricity, in order to avoid erroneously displaying a character on screen.
In order to check an error in the character signal, a parity bit has generally been used. Since the parity bit can merely reduce the number of occurrences of an error, however, a character may be wrongly displayed on screen when a character signal having an error is determined as not having an error using the parity bit.
The microcomputer 1 of the conventional character display apparatus shown in FIG. 1 transfers a display character 1 and a display character 2 to the character generator 3 (100,101) and then outputs blank data 1-blank data 8 as an erasure counter.
Namely, each time a sub-routine is called, the microcomputer 1 transfers the blank data(102-111) as altered lines. Accordingly, the conventional character display apparatus has a disadvantage, in that too much load is placed on the microcomputer 1.